In the early 1970's network broadcasters saw a need for their local television stations to have an automated master control system that worked hand in hand with a traffic and sales system. The initial goal was to create sales orders and a schedule that could then be formatted into a file that could be loaded into a computer system. This computer would then control the systems used in the master control operation. Finally the completed log with accurately logged air times and log discrepancies would be returned to the sales system allowing for an automated billing to clients. That traffic and sales system originally ran on a mainframe computer system. These two systems would later become the Integrated Broadcast System (IBS) and Real-Time (RT) system respectively.
Network broadcasters such as CBS also own and operate many local affiliate stations throughout the country. Each of these local stations broadcasts the network master schedule in addition to local programming (e.g., local news) that does not come from the network. The master schedule is a detailed down to the second account of that day's programming. Programming may include television programs, advertisement spots, and promotions of network programs hereinafter referred to as programs and spots. Television programs may be pre-recorded or live.
Today, consumers may obtain television service from one of many different alternatives. In addition to over-the-air (OTA) reception of locally broadcast television signals, consumers may receive television programming through service providers such as cable television service providers, satellite television service providers, and television over telephone line service providers. A network delivers its broadcast schedule and content to each of its local stations (e.g., affiliates). The local stations must then insert the various spots into the schedule along with the programs and distribute a broadcast signal to each of the television service providers as well as broadcast the signal over-the-air. The spots must be inserted during local station breaks at exactly the right moment by the local station to avoid even momentary black screen conditions that may be caused when transitioning from the program to a local station break.
For many programs, the network may tweak the schedule by adjusting when the station breaks may occur for a given program. Often these adjustments are made very close to the actual airing of the program. The local stations must be able to adjust to the revised schedule to ensure the station breaks are updated accordingly. A network video signal is typically sent to the local station via a satellite connection which creates a slight albeit noticeable delay. The network video signal may be comprised of the video signal itself (e.g., content of a program) as well as a control signal. The control signal may include a trigger control signal that marks a point in the program to indicate that a station break will occur within the program in x seconds. The trigger control signal, however, does not factor a local delay (δ) that may occur as a result of the transmission time from network facility to local station.
Accounting for the delay is necessary to avoid unwanted black screen moments when the network video signal and local schedule are not totally in sync with one another.